1. Field of the Invention
The invention relates to a process for manufacturing microstructured bodies with structural depths ranging from several microns to several millimeters, with lateral dimensions in the micron range, by irradiation of polymers with X-rays and subsequent development with suitable developing media
2. Description of the Background
In microelectronics, the technological advances of increasing miniaturization and integration have led to a myriad new products. Compared to other sectors, the advances in miniaturization in microelectronics in just a few recent years have been remarkable. Indications are that in the future other microtechniques as well will become important. Areas which might be mentioned are micromechanics, integrated optics, and microfluidics. Such technologies, in combination with microelectronics, offer the possibility of numerous novel electronic, optical, biological, and mechanical functional elements of revolutionary types. The highly productive manufacturing methods of semiconductor technology can be exploited in a wide range of applications in the mass production of miniaturized non-electronic components, modules, and subsystems. Classical methods of fine fabrication for micromechanics have been strengthened and combined with appropriately modified methods from semiconductor fabrication, to go beyond the constraints of planar silicon technology and make available novel options in the forning of materials, applicable for numerous shapes and configurations, and numerous materials. An advance of this nature is the LIGA method (Lithographie-Galvanoformung-Abformung (i.e., lithography-galvanoforming-molding)), which combines fabrication steps involving lithography, galvanoforming (electrochemical forming), and molding, and is described in German Patent Application No. 41 42 001, incorporated herein by reference. The method was developed at Kernforschungszentrum Karlsruhe (the Karlsruhe, Germany Nuclear Research Center). The essential fabrication step of the original LIGA method is the structurally accurate irradiation of a polymer material. The basic practicability of the LIGA method can be demonstrated by microstructures produced in a specially manufactured polymethyl methacrylate (PMMA). A number of other plastics have been developed with the aim of compatibility with forming techniques employing X-ray irradiation. Among these one might mention polyoxymethylene (POM), and polyesters, particularly polyglycolides and polylactides, as described in German Patent Application No. 41 41 352 A1.
The use of "SU8" epoxy photoresist for microstructuring using UV lithography has been described in a number of publications: Despont, M., Lorenz, H., Fahrin, N., Brugger, J., Renaud, P., and Vettiger, P., 1997, "High-aspect-ratio, ultrathick, negative-tone near-UV photoresist for micro electro mechanical systems (MEMS) applications", in "Proc. of the 10th IREE International Workshop on Micro Electro Mechanical Systems (MEMS '97)", Jan. 26-30, 1997, Nagoya, Japan; and Lee, La Bianca, et al., "Micromachining applications of a high resolution ultrathick photoresist", J.Vac.Sci.Technol., B13(6), November/December 1995, all of which are hereby incorporated by reference. In addition, epoxide mixtures are used for the encapsulation of, e.g., microelectronic, electronic, or optical components (see PROTAVIC brochure).
In the fabrication of complex three-dimensional structures with structural depths ranging from several microns to several millimeters, using the LIGA method, it has been found that the existing plastics require a substantial amount of irradiation. It has also been found that in the development of irradiated polymer articles with a suitable developing medium the un-irradiated polymer regions tend to swell, wherewith the fine structures formed may be distorted or otherwise faulty. Further, the swollen polymer regions can result in stress cracking when the material is dried, thereby rendering the microstructure bodies unsuitable for electrochemical processing. Another problem is that for some of the plastics used, the processing is complex and expensive. This is true of polylactides and polyglycolides, wherewith costly stamping steps must be employed to apply the materials to substrates prior to irradiation.
UV-hardening coating systems may be used for fabricating microstructures. With these it has been impossible with the means at hand to achieve the level of submicron precision and accuracy which is often needed for optical and fluidic components; the difficulties are attributed to diffraction, scattering, and interference effects on the irradiating light (wavelengths 300 mn to 460 mn), if the coating thicknesses are in the micron and millimeter range.